One known type of information storage device is a disk drive device that uses magnetic media to store data and a movable read/write head that is positioned over the media to selectively read from or write to the disk.
Consumers are constantly desiring greater storage capacity for such disk drive devices, as well as faster and more accurate reading and writing operations. Thus, disk drive manufacturers have continued to develop higher capacity disk drives by, for example, increasing the density of the information tracks on the disks by using a narrower track width and/or a narrower track pitch. However, each increase in track density requires that the disk drive device have a corresponding increase in the positional control of the read/write head in order to enable quick and accurate reading and writing operations using the higher density disks. As track density increases, it becomes more and more difficult using known technology to quickly and accurately position the read/write head over the desired information tracks on the storage media. Thus, disk drive manufacturers are constantly seeking ways to improve the positional control of the read/write head in order to take advantage of the continual increases in track density.
One approach that has been effectively used by disk drive manufacturers to improve the positional control of read/write heads for higher density disks is to employ a secondary actuator, known as a micro-actuator, that works in conjunction with a primary actuator to enable quick and accurate positional control for the read/write head. Disk drives that incorporate micro-actuators are known as dual-stage actuator systems.
Various dual-stage actuator systems have been developed in the past for the purpose of increasing the access speed and fine tuning the position of the read/write head over the desired tracks on high density storage media. Such dual-stage actuator systems typically include a primary voice-coil motor (VCM) actuator and a secondary micro-actuator, such as a PZT element micro-actuator. The VCM actuator is controlled by a servo control system that rotates the actuator arm that supports the read/write head to position the read/write head over the desired information track on the storage media. The PZT element micro-actuator is used in conjunction with the VCM actuator for the purpose of increasing the positioning access speed and fine tuning the exact position of the read/write head over the desired track. Thus, the VCM actuator makes larger adjustments to the position of the read/write head, while the PZT element micro-actuator makes smaller adjustments that fine tune the position of the read/write head relative to the storage media. In conjunction, the VCM actuator and the PZT element micro-actuator enable information to be efficiently and accurately written to and read from high density storage media.
One known type of micro-actuator incorporates PZT elements for causing fine positional adjustments of the read/write head. Such PZT micro-actuators include associated electronics that are operable to excite the PZT elements on the micro-actuator to selectively cause expansion or contraction thereof. The PZT micro-actuator is configured such that expansion or contraction of the PZT elements causes movement of the micro-actuator which, in turn, causes movement of the read/write head. This movement is used to make faster and finer adjustments to the position of the read/write head, as compared to a disk drive unit that uses only a VCM actuator. Exemplary PZT micro-actuators are disclosed in, for example, JP 2002-133803; U.S. Pat. Nos. 6,671,131 and 6,700,749; and U.S. Publication No. 2003/0168935, the contents of each of which are incorporated herein by reference.
FIGS. 1 and 2 illustrate a conventional disk drive unit and show a magnetic disk 101 mounted on a spindle motor 102 for spinning the disk 101. A voice coil motor arm 104 carries a head gimbal assembly (HGA) 277 that includes a micro-actuator with a slider 203 incorporating a read/write head. A voice-coil motor (VCM) is provided for controlling the motion of the motor arm 104 and, in turn, controlling the slider 203 to move from track to track across the surface of the disk 101, thereby enabling the read/write head to read data from or write data to the disk 101.
Because of the inherent tolerances (e.g., dynamic play) of the VCM and the head suspension assembly, the slider cannot achieve quick and fine position control which adversely impacts the ability of the read/write head to accurately read data from and write data to the disk when only a servo motor system is used. As a result, a PZT micro-actuator, as described above, is provided in order to improve the positional control of the slider 203 and the read/write head. More particularly, the PZT micro-actuator corrects the displacement of the slider on a much smaller scale, as compared to the VCM, in order to compensate for the resonance tolerance of the VCM and/or head suspension assembly. The micro-actuator enables, for example, the use of a smaller recording track pitch, and can increase the “tracks-per-inch” (TPI) value for the disk drive unit, as well as provide an advantageous reduction in the head seeking and settling time. Thus, the PZT micro-actuator enables the disk drive device to have a significant increase in the surface recording density of the information storage disks used therein.
FIG. 2a shows a conventional U-shaped micro-actuator design. In FIG. 2a, the micro-actuator 105 has a ceramic frame 100, with side arms 107 and 108 having PZT elements 107a and 108a respectively mounted thereon. The PZT micro-actuator 105 is coupled to the tongue of a suspension on the HGA at the bottom of arm 100. A parallel gap (not shown) exists, allowing the micro-actuator 105 to smoothly displace the slider 203 when a voltage is applied to one or more of the PZT elements 107a and 108a. 
FIG. 2b shows another conventional U-shaped micro-actuator design. In FIG. 2b, the micro-actuator 105′ has a metal frame 213, with top support arm 214, bottom support arm 215, and side arms 211 and 212 having PZT elements 207 and 208 respectively mounted thereon. The bottom support arm 215 is mounted on the suspension tongue. A parallel gap (not shown) exists, allowing the micro-actuator 105′ to smoothly displace the slider 203 when a voltage is applied to one or more of the PZT elements 207 and 208.
FIG. 2c illustrates the head gimbal assembly (HGA) 277 incorporating a dual-stage actuator in the conventional disk drive device of FIGS. 1 and 2. More particularly, FIG. 2c is an enlarged perspective view of a conventional HGA of the disk drive from FIGS. 1 and 2. The micro-actuator of FIG. 2b located on a HGA. It will be appreciated that the micro-actuator of FIG. 2a also could be located on the HGA of FIG. 2c, and thus a corresponding description is omitted. In brief, electrical connection balls 109 may be used to operably couple the micro-actuator 105′ to the suspension traces 117 on each one side of the PZT elements 207 and 208. The electrical connection balls 109 may be formed by, for example, gold ball bonding (GBB), solder ball bonding (SBB), or the like. In additional, the slider 203 is inserted and mounted on the top support 214 of the metal frame 213, and there are a plurality of electrical connection balls (coupled by GBB, SBB, or the like) to operably couple the slider 203 to the suspension traces 110 for electrical connection with the read/write transducers. When an actuating voltage is applied through the suspension traces 117, PZT elements 207 and/or 208 on side arms 211 and/or 212 will expand and/or contract, causing side arm 211 and/or 212 to bend in a common lateral direction. Thus, the slider 203 undergoes a lateral translation because it is attached to the two side arms. Accordingly, it is possible to attain a fine head position adjustment.
Because micro-actuators have become so prevalent in the industry and so important to the proper functioning of hard disk drives, a need has developed in the art relating to how to identify problems with and/or failures of the PZT element. Such problems may include, for example, the presence of micro-cracks, PZT element deformations, etc. Traditional techniques for detecting problems with the PZT elements involve visual inspection of the PZT. Obviously, these techniques suffer several disadvantages. For example, visual inspection simply is not feasible given, for example, the size and complexity of the PZT elements and HGAs.
Other techniques involve introducing a voltage into one PZT elements and performing capacitance measurement and/or resonance measurement using Laser Doppler Vibrometers (LDV) on another PZT element to detect mechanical resonance characteristics and, in particular, deviations from a predetermined norm. One example is disclosed in U.S. Publication No. 2003/0076121, the contents of which is incorporated in its entirety herein by reference.
In particular, FIG. 3a is a prior art test device 300 for detecting errors on an HGA having two PZT elements. The test device 300 includes a user interface 314 having an associated input mechanism 318 and a display 316, a test control processor 312, a signal generator 308, and a signal analyzer 310. The signal generator 308 is electrically connected (304) to the first of the PZT elements 207 of the micro-actuator of the first arm of the HGA. The signal analyzer 310 is electrically connected (306) to the other PZT element 208 of the micro-actuator of the second side arm. The test control processor 312 instructs the signal generator 308 to output a reference signal at a predetermined voltage (e.g., a swept, sine, period chirp, random noise, etc.). This reference signal will excite the PZT element 207 and cause the first side arm to bend. Because the first arm is coupled to the second arm and the second PZT element is located on the second arm, the second PZT element 208 will bend, thereby generating a response voltage in the PZT element 208. The signal analyzer 310 may detect the response voltage, and the test control processor 312 may compare the reference signal characteristics and the response signal characteristics to predict the characteristics of the micro-actuator.
FIG. 3b is illustrative output from the prior art system of FIG. 3a. The comparison data may shown as a bode plot, which is a convenient way to represent the steady state frequency response of an electronic filter. The graph plots the log of the gain against the log of the frequency. R1 is the output of the electrical signal of the PZT element 207 or 208, and R2 is the expected response signal. If the response signal R1 and the known expected response signal R2 do not match (e.g., the main peak frequency shifts, the gain amplitudes differ, etc.), then there may be PZT element damage or defect because the response characteristics of the PZT elements have changed.
These conventional methods of capacitance and LDV measurement work fairly well for HGAs having two PZT elements in the structure. Unfortunately, they may not work at all when there is a single PZT element in the system. Such a case may arise in the hard disk drive sensor system. Thus, it will be appreciated that there is a need in the art for an improved system that does not suffer from one or more of the above-mentioned drawbacks.